Super-hard materials, such as diamond or cubic boron nitride (CBN), have superior wear resistance and are commonly used as cutting elements for cutting or drilling applications. In these applications, a compact of polycrystalline diamond or CBN is commonly bonded to a substrate material (e.g., cemented metal carbide) to form a cutting structure. A compact is a polycrystalline mass of super-hard particles, such as diamond or CBN, that are bonded together to form an integral, tough, coherent, and high-strength mass. The substrate material generally is selected from the group consisting of tungsten carbide, titanium carbide, tantalum carbide, and mixtures thereof. The substrate material further contains a metal-bonding material selected from the group consisting of cobalt, nickel, iron, and mixtures thereof. The metal bonding material is normally 6 to 25 percent of the material by weight. Such compacts and other super-hard structures have been used as blanks for cutting tools, drill bits, dressing tools, wear parts, and rock bits. Additionally, compacts made in a cylindrical configuration have been used to make wire drawing dies.
Various methods have been developed to make polycrystalline diamond or CBN compacts. One such method involves subjecting a mass of separate crystals of the super-hard abrasive material and a catalyst metal to a high pressure and high temperature (HPHT) process which results in inter-crystal bonding between adjacent crystal grains. The diamond or CBN materials are thermodynamically stable under the pressure and temperature conditions used in HPHT. The catalyst metal may be a cemented metal carbide or carbide-molding powder. A cementing agent also may be used that acts as a catalyst or solvent for diamond or CBN crystal growth. The cementing agent generally has been selected from cobalt, nickel, and iron when diamonds are used as the super-hard abrasive material. Aluminum or an aluminum alloy generally is used as a cementing agent when CBN is used as the super-hard material. The catalyst metal preferably is mixed with the super-hard crystals (e.g., in powder form).
Although the catalyst may be mixed in powder form with the super-hard crystals, no attempt is made to minimize the formation of clusters of super-hard crystals. As a result, the compacts produced by this method commonly are characterized by diamond-to-diamond or CBN-to-CBN bonding (i.e., inter-crystal bonding between adjacent grains). This maximization of inter-crystal bonding between adjacent grains is an objective in making super-hard compacts. Typically, a diamond compact formed in the presence of cobalt contains multiple clusters of diamond grains with each cluster containing more than one (e.g., 3 to 6) diamond grains. These clusters connect with each other and form a network of diamond grains. In a typical diamond compact, diamond grain-to-grain contiguity is greater than 40%. The diamond grain-to-grain contiguity refers to the percentage of continuous diamond phase in a given direction within a diamond compact, and is indicative of the extent of diamond-diamond contact in the diamond compact. The cobalt phase typically is not a continuous matrix. Instead, pools of cobalt are distributed in the spaces formed by the diamond clusters. The average size of the cobalt pools typically is larger than the average size of the diamond grains.
With this microstructure, the compacts are extremely wear resistant, but relatively brittle. Once a crack starts, it can propagate through the compact and eventually result in failure of the part. This is particularly true in the case of petroleum or rock drill bits, in which a massive failure of the diamond layer of an insert made of a polycrystalline diamond compact can lead to damage of the other cutters on the bit or the bit body.
Additionally, diamond or CBN compacts are relatively expensive to manufacture with the high pressure/high temperature process. Further, the size of the diamond or CBN compacts is limited by the dimensions of the press cell. Typically, only a few pieces, each having a cross-section of less than 1 inch, can be processed in a press cell, while the largest piece that presently can be processed has a cross-section of less than 2 inches.
For the foregoing reasons, there exists a need for a wear-resistant material that utilizes the wear resistance of diamond or CBN materials while possessing a higher toughness than previously typical of diamond or CBN compacts. Further, it is desirable that the method of manufacturing such a composite material be capable of producing parts that are larger than 2 inches in cross-section.